Forming method of composite material special-shaped hollow pipe fitting

Abstract

The invention relates to a forming method of a composite material special-shaped hollow pipe fitting, and belongs to the technical field of pipe fitting preparation. The preparation method comprises the following steps that S1, an SMP material is used for preparing a core mold; s2, prepreg is laid outside the core mold, and the core mold is placed in a vacuum bag to be vacuumized according to the set number of layers of the prepreg; s3, an air bag is placed in the core mold, the whole device is placed in a rigid mold, the air bag is inflated to the set air pressure after mold closing, and then heating and curing are conducted; and S4, after the product with the core mold is separated from the rigid mold, the product is evenly heated to the temperature above the glass transition temperature of the SMP material, the softened core mold is removed, and the product is obtained. After the air bag is placed in the core mold, the shape of the core mold can be supported by means of the air bag, so that the core mold can still keep a fixed outline even if the core mold is heated to the glass-transition temperature or above in the heating and curing process, and product forming is achieved through the core mold and the rigid outer mold together.

Description

Technical Field

[0001] The invention belongs to the technical field of pipe fitting preparation, and in particular relates to a forming method of a composite material special-shaped hollow pipe fitting. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] There are a large number of hollow pipes used in rail vehicles. Special-shaped hollow pipes are mostly made of metal welding. With the development of technology and the requirement of lightweight vehicles, more and more pipes are made of composite materials. There are two main manufacturing processes for special-shaped pipes made of composite materials: one is to lay out the pieces on the metal female mold, and then assemble the formed areas in blocks; the other is to use core molds to assist in forming. The types of core molds include metal core molds, rubber core molds, EPS latex core molds, and soluble core molds. Different core molds have different advantages and disadvantages. Overall, the manufacturing process is numerous, the molding cycle is long, and the manufacturing cost is high.

[0004] The Chinese patent with application number 2019103291834 provides a method for forming composite material special-shaped tubes by using shape memory material to prepare a core mold, laying prepreg on the core mold, placing it in a rigid mold, and pressurizing and curing it. However, the core mold prepared by it needs to be provided with a plug and an inflation tube, and the inside of the core mold is inflated. When the core mold is a special-shaped structure, or the thickness is not equal at each position, or even sharp corners need to be set, the airtightness requirement undoubtedly increases the difficulty of preparing the core mold. And due to the limitations of 3D printing and material technology, when printing large core molds, the parts with excessive curvature of the outer surface can only be point-supported on the printing table, which is difficult to fix on the printing table. Even if the support structure is increased, it is still difficult to achieve the target accuracy, which affects the application in special-shaped hollow pipe fittings. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a molding method for composite material special-shaped hollow pipe fittings, wherein a core mold is made of shape memory polymer (SMP), multiple layers of prepreg are laid on the outside of the core mold, vacuum is drawn during the laying process, and then an air bag is filled in the core mold. The whole is pressurized in a rigid outer mold, thereby improving the efficiency of the one-piece molding of the special-shaped hollow structure of the composite material.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] A method for forming a composite material special-shaped hollow pipe comprises the following steps:

[0008] S1. Prepare a core mold using SMP material;

[0009] S2. Lay the prepreg outside the core mold, place it in a vacuum bag and evacuate it after laying a set number of layers;

[0010] S3, placing an air bag in the core mold, placing the entire device in a rigid mold, inflating the air bag to a set air pressure after closing the mold, and then heating and curing;

[0011] S4. After the product with the core mold is removed from the rigid mold, it is uniformly heated to above the glass transition temperature of the SMP material, and the softened core mold is removed to obtain the product.

[0012] The beneficial effects of the present invention are:

[0013] The present invention utilizes SMP shape memory polymer, and can utilize 3D printing technology to prepare high-precision shape structure. SMP shape memory polymer has rigidity below the glass transition temperature, and can be used as a core mold to support the paving of prepreg. After placing an airbag in the core mold, the shape of the core mold can be supported by the airbag, so that the core mold can still maintain a fixed profile even if it is heated to above the glass transition temperature during the heating and curing process, and realize the forming of the product together with the rigid outer mold. During the paving process, the interlayer bubbles of the prepreg are discharged by vacuuming operation to reduce the defects of the side wall of the product. The whole process reduces the mold operation steps under the premise of ensuring the internal support effect of the core mold, which can reduce the complexity of the product manufacturing process and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0015] Figure 1 It is a structural schematic diagram of the sand spreading arm in a specific implementation manner.

[0016] Figure 2 It is a structural schematic diagram of the core mold in a specific implementation manner.

[0017] Figure 3 It is a schematic diagram of the device structure during vacuum operation in a specific implementation manner.

[0018] Among them, 1. core mold; 2. release cloth; 3. prepreg paving layer; 4. isolation film; 5. breathable felt; 6. vacuum bag. DETAILED DESCRIPTION

[0019] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0020] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0021] A method for forming a composite material special-shaped hollow pipe comprises the following steps:

[0022] S1. Prepare a core mold using SMP material;

[0023] S2. Lay the prepreg outside the core mold, place it in a vacuum bag and evacuate it after laying a set number of layers;

[0024] S3, placing an air bag in the core mold, placing the entire device in a rigid mold, inflating the air bag to a set air pressure after closing the mold, and then heating and curing;

[0025] S4. After the product with the core mold is removed from the rigid mold, it is uniformly heated to above the glass transition temperature of the SMP material, and the softened core mold is removed to obtain the product.

[0026] Through the above steps, the core mold can maintain rigidity during the paving process and has the ability to deform during the demoulding process, so as to reduce the difficulty of preparing the core mold and reduce the operating steps in the product forming process.

[0027] Optionally, the core mold is a shell-like structure, and the outer thickness of the product part line is 1.5 to 2 times the thickness of the plane wall. This design can make the core mold a locally reinforced unequal thickness structure, which is suitable for positions with smaller curvatures of special-shaped hollow pipes, improves the rigidity of the special-shaped core mold, and prevents damage to sharp corners or corners during paving or demolding.

[0028] Optionally, in S1, the core mold is prepared by 3D printing, and an opening is left at the end for placing the airbag. 3D printing is suitable for the preparation of special-shaped hollow pipes. A hollow shell structure can be prepared using SMP wire as raw material, and a cavity is left inside for placing the airbag in subsequent steps.

[0029] Optionally, in S2, before laying the prepreg, a release cloth is pasted on the outside of the core mold; since there will be residual printing lines on the surface of the core mold obtained by 3D printing, these printing lines will be transferred to the inner surface of the special-shaped hollow pipe during the heating and deformation process of the prepreg, so the release cloth is first pasted on the surface of the core mold to cover the printing lines, so that the inner surface of the prepared special-shaped hollow pipe is smooth, and the release cloth can also reduce demolding resistance.

[0030] Optionally, in S2, the prepreg is laid in an overlapping manner in a room temperature environment, and the joints of each laid layer do not overlap; the overlapping method is beneficial to improving the uniformity of the prepreg layer and reducing the performance weak points caused by the joints.

[0031] Optionally, in S2, before placing it in the vacuum bag, an isolation film and a breathable felt are laid in sequence on the outside of the prepreg. After the vacuuming is completed, the breathable felt and the isolation film are removed, and the prepreg is continued to be laid. This step is used to exhaust the gas in the prepreg layer. Since the special-shaped hollow pipe fittings usually need to be assembled and connected with other structures, higher strength is required, so the thickness of the paving layer is relatively large. It is easy for multi-layer paving to have residual gas inside. Therefore, it is necessary to vacuumize multiple times during the paving process to remove bubbles in the wrinkled positions or seams. Isolation films and breathable felts are commonly used in vacuum film forming processes. They are used here in the present invention to utilize their exhaust function to form a dense prepreg paving layer.

[0032] Optionally, in S2, the vacuuming operation is performed on a constant temperature heating table, and the heating temperature is lower than the glass transition temperature of the SMP material. At this temperature, the rigidity of the core mold remains unchanged and the supporting effect can be maintained, while the prepreg is softened, thereby improving the R corner laying quality.

[0033] Optionally, in S3, the airbag is inflated to a pressure of 0.4 to 0.6 MPa. After the airbag is inflated, the supporting force is transmitted to the prepreg paving layer through the softened core mold, and the molding of the special-shaped hollow pipe is completed in combination with the rigid mold on the outside. Since the bubbles in the prepreg paving layer have been removed by the previous vacuum operation, in S3, a dense prepreg layer can be obtained under the internal and external pressures of the airbag and the rigid mold.

[0034] Optionally, in S4, the gas in the airbag is released, the airbag is removed, and then the product and the core mold are uniformly heated to above the glass transition temperature of the SMP material; when removing the airbag, in order to avoid damage to the core mold, it is necessary to operate under conditions below the glass transition temperature of the SMP material, so that the rigid core mold and the flexible airbag are separated, and then the core mold is heated to above the glass transition temperature to allow the core mold to be deformed. Since a release cloth is attached to the surface of the core mold, it can be smoothly withdrawn from the end opening of the rigid special-shaped hollow pipe, and then the release cloth is peeled off from the surface of the core mold to obtain a deformed core mold.

[0035] Optionally, the method further includes step S5, placing the deformed core mold into a reshape mold, placing an airbag in the core mold, inflating the core mold at a temperature higher than the glass transition temperature of the SMP material, and then cooling it to room temperature; at this time, the role of the airbag is to accelerate the reshape of the core mold and make its surface smooth for subsequent use.

[0036] Example 1

[0037] The locomotive sand spreading device is used to spread sand from the rail vehicle to the rail surface to increase the friction between the rail surface and the wheels, and prevent the train from slipping or the wheels from spinning in bad weather such as rain and snow. The sand spreading arm is one of the components of the locomotive sand spreading device, and its shape is like Figure 1 As shown, it is a special-shaped hollow pipe fitting, the interfaces at both ends of which are rectangular, the joint direction of one end is vertical, and the joint direction of the other end is horizontal, so as to be connected with other parts of the sand spreading device. The central axis of the sand spreading arm is twisted in space according to the design requirements, and the pipe diameter changes at the set position. The product part line (the part line in the drawing refers to the outer contour of the product, corresponding to the groove on the mold surface), and the mold outside the product part line is more deformed, the local force is large and it is easy to be damaged. It is not easy to achieve high precision requirements using only the external mold, and the preparation is difficult.

[0038] The SMP shape memory polymer (SMP material) used in this embodiment is a polyurethane SMP material with a glass transition temperature of about 60°C, that is, it is rigid below 60°C, and its shape is easily changed above 60°C, and it can restore its shape when the temperature drops below 60°C.

[0039] A method for preparing a sand spreading arm comprises the following steps:

[0040] S1. Prepare a core mold using SMP material;

[0041] S2. Lay the prepreg outside the core mold, place it in a vacuum bag and evacuate it after laying a set number of layers;

[0042] S3, placing an air bag in the core mold, placing the entire device in a rigid mold, inflating the air bag to a set air pressure after closing the mold, and then heating and curing;

[0043] S4. After the product with the core mold is removed from the rigid mold, it is uniformly heated to above the glass transition temperature of the SMP material, and the softened core mold is removed to obtain a sand-spreading arm product.

[0044] In the above method, the SMP core mold has shape memory characteristics. When it is above the glass transition temperature, it is easy to change the shape and demold in the special-shaped hollow structure. After demolding, its shape can be restored below the glass transition temperature, so that the core mold can be reused and the cost of use is reduced.

[0045] In S1, the core mold is prepared by 3D printing method, and the shape of the core mold is as follows Figure 2 As shown, the core mold is a shell-like structure with an opening at the end for placing the airbag. In order to ensure the demoulding properties of the core mold, the wall thickness of the core mold is 2mm. In order to prevent the corners of the core mold from cracking during paving and demoulding, the thickness of the product parts line is 4mm, that is: the core mold has a local reinforcement structure, and its wall thickness varies depending on the position.

[0046] In S2, before laying the prepreg, a release cloth is pasted on the outside of the core mold; since the 3D printing process easily leaves printing lines on the surface, in order to prevent the printing lines from being transferred to the inner surface of the product during the curing process, and to prevent the printing lines and the inner surface of the product from biting each other and hindering demolding, it is necessary to paste a polytetrafluoroethylene adhesive release cloth on the outer surface of the core mold to improve the surface quality of the core mold.

[0047] In S2, the cut T300 woven cloth, T700 unidirectional tape, and glass fiber prepreg are laid in an overlapping manner according to the order and laying angles shown in Table 1.

[0048] Table 1 Composite material sand spreading arm layer table

[0049] Number of layers Material Specifications angle Number of layers Material Specifications angle 1 3K twill weave fabric 0 / 90° 17 T700 unidirectional belt 0° 2 3K twill weave fabric 0 / 90° 18 T700 unidirectional belt 90° 3 3K twill weave fabric 0 / 90° 19 T700 unidirectional belt ±45° 4 Fiberglass Woven Cloth 0 / 90° 20 T700 unidirectional belt 0° 5 Fiberglass Woven Cloth ±45° 21 T700 unidirectional belt 90° 6 Fiberglass Woven Cloth 0 / 90° 22 T700 unidirectional belt ±45° 7 Fiberglass Woven Cloth ±45° 23 T700 unidirectional belt 0° 8 T700 unidirectional belt 0° 24 T700 unidirectional belt 90° 9 T700 unidirectional belt 90° 25 T700 unidirectional belt ±45° 10 T700 unidirectional belt ±45° 26 Fiberglass Woven Cloth 0 / 90° 11 T700 unidirectional belt 0° 27 Fiberglass Woven Cloth ±45° 12 T700 unidirectional belt 90° 28 Fiberglass Woven Cloth 0 / 90° 13 T700 unidirectional belt ±45° 29 Fiberglass Woven Cloth ±45° 14 T700 unidirectional belt 0° 30 3K twill weave fabric 0 / 90° 15 T700 unidirectional belt 90° 31 3K twill weave fabric 0 / 90° 16 T700 unidirectional belt ±45° 32 3K twill weave fabric 0 / 90°

[0050] During the laying process, cold extraction is performed every three layers. Cold extraction refers to the operation of vacuuming the laid prepreg layer below the glass transition temperature. Before placing the core mold and the outer layer of the laid prepreg into the vacuum bag, first lay the isolation film and breathable felt on the outside of the prepreg in sequence, and then place the entire device into the vacuum bag. At this time, Figure 3 As shown, the innermost layer is the core mold 1, and from the inside to the outside are the release cloth 2, the prepreg paving layer 3, the isolation film 4, the breathable felt 5 and the vacuum bag 6; the vacuum operation is performed on a constant temperature heating table, and the heating temperature is lower than the glass transition temperature of the SMP material; during the process, the gas remaining in the paving layer 3 or the gas remaining in the paving folds is discharged, and then is drawn away through the breathable felt 5 to form a dense paving layer to avoid the generation of defects within the layer.

[0051] In S3, the airbag uses a nylon pressurized air bag, which is inflated to a pressure of 0.4-0.6 MPa, so that the outer wall of the airbag fits tightly with the inner surface of the core mold to provide support inside, and the extruded prepreg is formed between the rigid mold and the fixed-shape core mold; the curing process includes: the first stage is heated to 80°C at 2°C / min and kept warm for 30 minutes; the second stage is heated to 120°C at 1°C / min and kept warm for 30 minutes; the third stage is naturally cooled to room temperature; in this process, although the core mold softens and loses its support function above the glass transition temperature, the airbag is The bladder can provide internal support and combine with the external rigid mold to complete the solidification and forming process of the sand-spreading arm product; and, since the core mold is a structure of unequal thickness, if an inflatable core mold is prepared directly, when the softened core mold is under internal and external pressures, the thick wall position and the thin wall position may move relative to each other, causing wrinkles on the inner surface of the product. By adding the airbag structure, since the surface expansion ability of the airbag is not strong and the surface area will not change under the action of air pressure, the airbag after fitting the core mold can prevent the local movement of the core mold through friction and adhesion, thereby obtaining better inner surface quality to reduce surface defects.

[0052] In S4, the gas in the airbag is released and the airbag is removed. At this time, the core mold is still in a rigid state after cooling. Then, the product and the core mold are evenly heated to a temperature above 60°C to soften the core mold, and the softened core mold is pulled out from the inside of the sand-spreading arm product. In this embodiment, the product that has not been removed from the core mold and the core mold are immersed in hot water at 60°C at the same time to achieve uniform heating. Then, the product is cut along the part line to obtain the following Figure 1 Sand spreading arm product shown with mounting holes and other features.

[0053] S5. Place the deformed core mold into a circular mold, place an air bag in the core mold, place the core mold, the circular mold and the air bag in a 60°C oven, inflate the air bag to restore the core mold to its original shape, and after cooling, the rigid core mold that has restored its original shape can be reused for the preparation of the sand spreading arm.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for forming a composite material special-shaped hollow pipe, comprising the following steps: S1. Prepare a core mold using SMP material; S2. Lay the prepreg outside the core mold, place it in a vacuum bag and evacuate it after laying a set number of layers; S3, placing an air bag in the core mold, placing the entire device in a rigid mold, inflating the air bag to a set air pressure after closing the mold, and then heating and curing; S4. After the product with the core mold is removed from the rigid mold, it is uniformly heated to above the glass transition temperature of the SMP material, and the softened core mold is removed to obtain the product.

2. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: The core mold is a shell-like structure, and the outer thickness of the product part line is 1.5 to 2 times the thickness of the flat wall.

3. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: In S1, the core mold is prepared by 3D printing method, and an opening is left at the end for placing the airbag.

4. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: In S2, before laying the prepreg, a release cloth is pasted on the outer side of the core mold.

5. The method for forming a composite material special-shaped hollow pipe according to claim 4, characterized in that: Before placing it in the vacuum bag, lay an isolation film and breathable felt on the outside of the prepreg in sequence. After the vacuum is completed, remove the breathable felt and isolation film and continue to lay the prepreg.

6. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: In S2, the vacuuming operation is performed on a constant temperature heating stage, and the heating temperature is lower than the glass transition temperature of the SMP material.

7. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: In S2, the prepreg is laid in an overlapping manner in a room temperature environment.

8. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: In S3, the airbag is inflated to a pressure of 0.4 to 0.6 MPa.

9. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: In S4, the gas in the airbag is released, the airbag is removed, and then the product and the core mold are uniformly heated to above the glass transition temperature of the SMP material.

10. The method for forming a composite material special-shaped hollow pipe according to claim 1, characterized in that: The method further includes step S5, placing the core mold into the reshaped mold, placing an air bag in the core mold, inflating the core mold at a temperature higher than the glass transition temperature of the SMP material to reshape the core mold, and then cooling the core mold to room temperature.

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